JohnDixson hinted at a story about the Paris air show that fits perfectly with this thread about flying backwards.
First, some aerodynamic background. The rotor does not know which way it's going, so that flying backwards is actually no different to the rotor than flying sideward, or forward. Where the rotor not attached to a fuselage you would feel perfectly comfortable at hundred knots backward. What does get you feeling funny on the controls is the effect the sideward or rearward flight has on the horizontal tail, the vertical tail and tail rotor. Basically, those tail feathers are like the feathers of a dart, and they try to force the aircraft to point its nose into the wind. Try throwing a dart backward, feathers first, and note how it flips forward. About halfway into its journey, it goes point first and sticks its nose into the wall. Your helicopter does the same thing, and you spend most of your effort in rearward flight fighting the horizontal and vertical tails. This makes your cyclic and pedals workload very high. Any missed timings on the controls, and the aircraft literally tries to swap ends. If it does so, it does so quickly and you are a passenger for a few seconds, usually an anxious passenger..
The most disturbing thing about rearward flight is how the horizontal tail tries to take over. Because the horizontal tail stabilizes your pitch axis in forward flight, it destabilizes the pitch axis in rearward flight. You can tell how strong this effect is when you recover from rearward flight and the nose pitches way down during the deceleration. While it's generally foolish to fly rearward at appreciable speed, doing a pedal turn in a brisk wind is the same thing.
Now on to Paris! It was 1993, and JohnDixson & I had brought our latest toys to the air show. He had the latest model UH 60L and I had the experimental demonstrator that we called the Fantail. A quick Google search of the Sikorsky fantail will show you a picture of the modified S 76B with the fan. It was the prototype for the Comanche, which proved the effectiveness of the yaw device.
We were at the Le Bourget heliport and flying back to Issi Les Moulineaux, diagonally across Paris. Flying with me in the fantail was Etienne Herrenschmidt, a fine test pilot – my counterpart at Eurocopter. We took off in formation with the Black Hawk, JohnDixson in the lead. I asked John to hold steady at 80knots, and then pressed full left pedal and popped the aircraft into rearward flight. As we trimmed in formation with the Black Hawk, he going forward, and we going backwards, Etienne whistled under his breath "Formidable!" We flew two thirds of the way around Paris backward!
I didn't feel brave enough to shoot a backward approach to the Issy heliport (not from a courage standpoint, more from a "Will he get thrown out of France?" standpoint) and so I swung the aircraft nose first on long final. Etienne was grinning ear to ear as we settled into a hover!
So much for backward flight transition!
how important is it to fly backward? For civil helicopters probably not very important, for military helicopters, it means you can point your weapons in seconds perhaps twice as fast as making a bank, so that large rearward flight speed envelopes might buy you the ability to finish your mission.
A vanilla video of the Fantail:
Sikorsky H-76 Eagle FANTAIL Demonstrator - YouTube
some Comanche sideward flight, similar to that we proved on the H76 Fantail:
RAH-66 COMANCHE - YouTube